1. Field of the Invention
The present invention relates to a coaxial type starter device wherein the armature rotary shaft of a motor is arranged in the same axial line as that of an operating shaft in an electromagnetic switch.
2. Discussion of Background
There has been known a coaxial type starter as shown in, for instance, Japanese Unexamined Patent Publication No. 195331/1988. FIG. 2 shows such a coaxial type starter, which includes a dc motor 1 which comprises a yoke 2 which provides an outer circumferential wall, permanent magnets 3 attached to the inner circumference of the yoke 2 with intervals in the circumferential direction, an armature 4 rotatably disposed at the center of the yoke 2 and a face type commutator 5 connected to an end of the armature 4.
The armature 4 in the dc motor 1 comprises a tubular armature rotary shaft 6 and an armature core 7 attached to the outer circumference of the rotary shaft 6. A radially enlarged cavity portion is formed in the inner circumference of the tubular armature rotary shaft 6, and a plurality of cam surfaces are formed in the cavity portion in its circumferential direction. The face type commutator 5 fitted to the outer circumference of the armature rotary shaft 6 at its one end, namely, at the left side in FIG. 2, has a number of segments which are arranged in a plane perpendicular to the armature rotary shaft 6 so that they perform current rectification by their sliding contact with a plurality of brushes 8. Each of the segments is connected with an end portion of the armature coil 9 wound around the armature core 7.
The brushes 8 are supported by brush holders 10 made of a resinous material which are arranged outside a rear bracket 2a which is formed integrally with the yoke 2 and which constitutes a part of an earth, or ground, circuit. The brushes 8 are forcibly pressed to the sliding surface of the commutator 5 by means of springs 11 through openings formed in the rear bracket 2a.
A bearing 12 is fitted to the inner circumferential surface of a central opening formed in the rear bracket 2a. The bearing 12 supports the rear end, i.e. the end facing the commutator, of the armature rotary shaft 6.
The brush holder 10 comprises a molded body in which a fixed contact 13 is insert-molded, the fixed contact 13 being connected to a terminal (not shown), and a terminal block 14 connected with a lead wire having a positive polarity which is connected to a brush 8 and a screw 15 which connects the terminal block 14 with the molded body.
The cam surfaces 6a formed in the radially enlarged cavity portion of the armature rotary shaft 6 constitute a part of an overrunning clutch means. Namely, a clutch inner 16 in a tubular form is inserted in the cavity of the armature rotary shaft 6, and the front end portion of which is supported by a bearing 19 which is fitted to the front bracket 17. The front end portion of the armature rotary shaft 6 is supported by a bearing 18 which is fitted to the outer circumference of an intermediate portion of the clutch inner 16. The front bracket 17 is attached to the front end of the yoke 2, and it is fixed to the rear bracket 2a by means of long bolts. A plurality of wedge-like spaces are defined by the outer circumferential surface of the clutch inner 16 and each of the cam surfaces 6a formed at the circumferential surface of the radially enlarged cavity portion of the armature rotary shaft 6. In each of the wedge-like spaces, there are provided rollers 20 which connect the cam surface 6a to the other circumferential surface of the clutch inner 16 and a spring (not shown) which presses the rollers 20 in the engaging direction. Thus, the overrunning clutch means is constituted by the cam surfaces 6a, the clutch inner 16, the rollers 20 and the compression springs. Further, the armature rotary shaft 6 performs the function of the clutch outer.
A pinion shaft 21 as a rotary output shaft is disposed in the inner passage of the clutch inner 16 having a tubular shape. The clutch inner 16 is interlocked with the pinion shaft 21 by means of a helical spline formed in their outer and inner circumferences so that a rotating force can be transmitted between them, and they can be relatively moved in the axial direction. A reference numeral 16a designates the helical spline of the clutch inner 16 and 21a, the helical spline of the pinion shaft 21.
A pinion 21b is formed integrally with the front end of the pinion shaft so that the pinion 21b can be engaged with the ring gear (not shown) of an engine. The pinion shaft 21 is supported by a bearing 22 which is firmly fitted to the inner circumference of the rear part of the clutch inner 16. A spring 24 to return the pinion 21 is arranged between a stop ring 23 which is fitted to the outer circumference of the rear end of the pinion shaft 21 and the bearing 22.
A recess 25 is formed at the rear end surface of the pinion shaft 21. A first holder 26 having a cylindrical shape with one end opened is loosely fitted to the recess 25. A steel ball 27 is disposed between the bottom of the the recess 25 and the closed end portion of the first holder 26 to provide a thrusting force.
An electromagnetic switch device 28 is connected to the outer portion of the rear bracket 2a by means of bolts 29. The electromagnetic switch device 28 comprises a casing 30, an exciting coil 32 wound around a plastic bobbin which is supported by front and rear cores 31a, 31b which form a magnetic circuit in association with the casing 30, a plunger 33 arranged in the central opening of the bobbin so as to be slidable and a moving assembly 34 attached to the plunger 33. The plunger 33 receives a pushing force by a coil spring 35 which is interposed between the plunger 33 and the front core 31a so as to return the plunger 33 to the original position as shown in FIG. 2 when a key switch is OFF.
The moving assembly 34 has a rod 36 as an operating shaft which has an end connected to the plunger 33 and the other end which opposes the first holder 26 disposed at the rear end of the pinion shaft 21.
A third holder 37 having an opening 37a which opens toward the side of the pinion shaft 21 is firmly attached to the outer circumference of the rod 36 at a position near the plunger 33. The third holder 37 supports at its outer circumference a movable contacter 38 having a movable contact 38c which is interposed between two insulating materials 38a, 38b, so as to be slidable along the outer circumference of the third holder 37. A second holder 39 is slidably fitted to the outer circumference of the other end of the rod 36 so as to be slidable in its axial direction. A spring 40 is interposed between the rear portion of the second holder 39 and the inner end surface of the opening 37a of the third holder 37 so that the pinion shaft 21 is pressed forwardly, i.e. on the right direction in FIG. 2. A spring 41 is interposed between the end surface of the other end of rod 36 and the inner end surface of the first holder 26 so that the pinion shaft 21 is pushed forwardly. Non-magnetic plate 42 closes the rear end of the casing 30, which functions as a stopper when the plunger 33 is returned backwardly and functions as the rear wall for the electromagnetic switch device 28.
A step portion having a reduced diameter 6b is formed at the outer circumference of the rear end portion of the armature rotary shaft 6. A cylindrical body 43 having an outer circumference which is subjected to a knuring operation for preventing the armature core 7 from turning is forcibly fitted to the outer circumference of the step portion 6b. The armature core 7 is forcibly fitted to the outer circumference of the cylindrical body 43, whereby the armature core 7 is integrally fixed to the armature rotary shaft 6. A hardening treatment is conducted to the armature rotary shaft 6 so as to have a strength necessary for supporting the structural elements.
The operation of the conventional coaxial type starter having the construction mentioned above will be described.
In a state of the key switch being OFF, the exciting coil 32 is not excited because no current is conducted. Since only the spring 35 acts on the plunger 33, the moving assembly 34 takes the backward position and the plunger 33 is in contact with the plate 42. At this moment, the fixed contact 13 is separated from the movable contact 38c, whereby the dc motor 1 is stopped. Also, the pinion shaft 21 is located at the rear position by the spring 24.
When the key switch is turned on, the exciting coil 32 is energized to move the plunger 33. Then, the moving assembly 34 is moved forwardly, and the movable contact 38c is brought to contact with the fixed contact 13. Accordingly, the current is supplied to the armature coil 9 through the brushes 8 and the commutator 5 to thereby start the dc motor 1.
On the other hand, the pinion shaft 21 is pushed forwardly by the springs 40, 41 of the moving assembly 34, and at the same time of starting the d.c. motor, the ring gear fixed to the outer circumference of the flywheel of the engine is interlocked with the pinion 21a. On the starting of the engine, the pinion shaft 21 and the clutch inner member 16 are reversely actuated through the ring gear, so that they are rotated at a speed faster than the revolution of the armature rotary shaft 6. Then, the engagement between the clutch inner member 16 and the armature rotary shaft 6 is released by the action of the overrunning clutch, so that the armature rotary shaft 6 becomes idling. When the key switch is turned off because the starting of the engine has been finished, the supply of the current is interrupted, and the moving assembly 34 is returned to the rear position along with the plunger 33 by the action of the spring 35 in the electromagnetic switch device 28. Accordingly, the pinion shaft 21 is also returned to the rear position by the action of the spring 24.
In the conventional coaxial type starter, however, there were the following problems.
(1) Since the armature rotary shaft 6 functioned as the clutch outer member of the overrunning clutch, there was no single assembly as the overrunning clutch. Accordingly, it was difficult to evaluate the function of the overrunning clutch because it was combined in the armature assembly 4. It was difficult to conduct quality control in manufacturing the overrunning clutch assembly.
(2) Efficiency in assembling the armature assembly was very poor because the armature rotary shaft 6 had a long and small axial bore. Since the armature coil projected in the axial direction of the armature 1, operations by fingers or jigs were difficult and it was also difficult to assemble thin rollers 20 to the armature rotary shaft 6.
(3) Since the overrunning clutch mechanism was arranged in the armature rotary shaft 6, there was a restriction that the outer diameter of the overrunning clutch mechanism could not be increased. Accordingly, a sufficient performance of the clutch could not be obtained. Namely, it could not be expected to greatly increase the effective length of the roller which increases the capacity because even when the length of the roller 20 was increased in its axial direction, there caused uneven contact to the cam surfaces 6a. Further, since there was a relation of the outer diameter of the clutch&gt;the length L in the axial direction of the clutch with respect to the capacity of the clutch, the increase of the length L adversely affected to the increase of the capacity.
(4) Further, the coaxial type starter is apt to increase the entire length in comparison with a biaxial type starter wherein the operating shaft of the electromagnetic switch device and the armature rotary shaft are arranged in different axial lines in a parallel relation. Accordingly, there has been a strong demand to reduce the entire length in consideration of mounting a starter on the engine. Accordingly, the above-mentioned problems 1 through 3 had to be solved without increasing the entire length of the starter.